Pulp and Paper Industry Questions and Answers

Answer: A

Correct answer: lignin

Wood is roughly cellulose fibres bonded together by lignin, and pulping is the operation of dissolving that lignin so the fibres separate. Cellulose is the product and must be preserved, hemicellulose is partly retained because it helps the fibres bond in the sheet, and the extractives are a minor fraction. Every pulping and bleaching decision is a compromise between removing lignin and damaging cellulose.

Answer: B

Knowing what each fraction does explains why yields differ so widely between mechanical and chemical pulping. Only the cellulose is wanted in full, and the others are removed to varying degrees. Yield follows directly from how much is dissolved.

Answer: C

Yields above ninety per cent are possible because nothing is dissolved away, but the retained lignin makes the paper weak and prone to yellowing. Newsprint is the classic product. Chemical pulping sacrifices half the wood for strength.

Answer: D

Both are true and the reason gives the mechanism: chemical pulps have the lignin removed and are far more stable, which is why archival papers are made from them rather than from groundwood. Old newspaper browns within a few years.

Answer: A

The first two are correct. The third is wrong, since mechanical action shortens and damages the fibres while kraft leaves them long and strong, which is exactly why kraft dominates packaging grades. Energy consumption is the other drawback of the route.

Answer: B

Correct answer: sodium hydroxide and sodium sulphide

That mixture is white liquor, and the sulphide is what makes the kraft process kraft - German for strong - since it accelerates delignification and leaves the fibres less damaged than soda alone would. The sulphite process uses bisulphite and sulphurous acid instead, and it was displaced by kraft on pulp strength and on chemical recovery.

Answer: C

The fibres survive the cook with their length and strength largely intact, which is what sacks and corrugated board need. The strength of the liquor is incidental to the name. Sack paper is the product it is named for.

Answer: D

Correct answer: 2 - 4 - 1 - 3

Chips are made and screened to a uniform size so they cook evenly, cooked in white liquor until the lignin is dissolved, washed so the pulp is separated from the spent black liquor, and the black liquor is then evaporated and burned to recover the chemicals. The recovery step comes last because it works on what the washing produced, and it is what makes the process economic.

Answer: A

Correct answer: evaporated and burned to recover chemicals

Black liquor carries the dissolved lignin and the spent cooking chemicals. Concentrated to about seventy per cent solids and burned in a recovery boiler, the organic content raises steam and the inorganic content leaves as a smelt of sodium carbonate and sodium sulphide. Over ninety-five per cent of the chemicals are recovered, and a kraft mill is usually a net exporter of energy as a result.

Answer: B

Both are true and the reason gives both benefits: a mill without recovery would have to buy fresh chemicals continuously and dispose of a heavily polluting liquor, neither of which is tolerable. The recovery boiler also raises most of the mill's steam.